Perforated material for Ventilation - EP

Hi everyone,
I’m running an energy simulation and I’m not sure how could I model a perforated material that will be used for ventilation. I tried to model the openings on Rhino and set it as airwalls but I wanted to know if it accounts for ventilation or if I should model it as windows that are always open and connect it to the Set EP Airflow Component.
Best regards,

Hi @Juliana ,

Good question. You definitely don’t want to use Air Walls here since they are only intended for the case of interior walls, where you have air mixing from one zone into another.

The way to model a perforated building envelope that is truest to how it actually perform is to use operable windows but you will likely want to adjust at least two properties in comparison to normal windows.

First, you should change them to have a construction that permits the same amount of sun as your perforated material. Next, you will probably want to decrease the the stackDischargeCoeff_ on the “Set EP Airflow” component to account for the friction that the air experiences as it passes through the perforations.

If you read the description there, it will give you discharge coefficients for both unobstructed windows (0.25) and windows with insect screens (0.17). I’m sure your perforations are closer to insect screens but you may have to use a bit of intuition to estimate a reasonable value for your type of perforations.

Hi @chris, thanks for the answer.

Actually by perforated material I meant something like the picture below. Is there a way to change the glazing to an opaque material or the windows will only accept glass materials?

I also tried to model it using the shade generator component but at least what I understood is that you can only use it connected to a window too, so I had the same problem.

I’m just trying to model an element that is not actually a window (there’s no glass on it) but it’s used for ventilation. The geometry would be exactly as what it’s shown on the picture.

Thanks and regards.

Hi @Juliana ,

So you can create a glass material that has 0 transmittance if you want to model a perforated envelope as completely opaque. Another strategy is to make a glass material with 1 transmittance (as it if is not there) and then you can model the opaque portions as blinds.

Given the amount to sunlight I see passing through that photo there, I would recommend that latter for your case as the EnergyPlus blinds material can account for the solar energy that makes it through the slats.

Guess that’s exactly what I needed.
Thank you!